Threshold for a sliding system



FIG. 1 is a perspective view of a threshold for a sliding system;

FIG. 2 is a front or back view thereof;

FIG. 3 is a left or right view thereof;

FIG. 4 is a top view thereof;

FIG. 5 is a bottom view thereof; and,

FIG. 6 is a perspective view thereof with a floor and a sliding door or window in broken lines for illustrative purposes only and form no part of the claimed design. 

CLAIM The ornamental design for a threshold for a sliding system, as shown and described. 